Driving methods for color display devices

ABSTRACT

The present invention provides driving methods for electrophoretic color display devices. The backplane system used for the driving methods is found to be simpler which renders color display devices more cost effective. More specifically, the driving method comprises first driving all pixels towards a color state by modulating only the common electrode, followed by driving all pixels towards their desired color states by maintaining the common electrode grounded and applying different voltages to the pixel electrodes.

This application claims the priority of U.S. Provisional Application No.61/824,928, filed May 17, 2013; the contents of which is incorporatedherein by reference in its entirety.

FIELD OF THE INVENTION

The present invention is directed to driving methods for color displaydevices. The methods can greatly reduce complexity of the active matrixbackplane used for this type of display devices.

BACKGROUND OF THE INVENTION

In order to achieve a color display, color filters are often used. Themost common approach is to add color filters on top of black/whitesub-pixels of a pixellated display to display the red, green and bluecolors. The biggest disadvantage of such a technique is that the whitelevel is normally substantially less than half of that of a black andwhite display, rendering it an unacceptable choice for display devices,such as e-readers or displays that need well readable black-whitebrightness and contrast.

SUMMARY OF THE INVENTION

A first aspect of the invention is directed to a driving method for adisplay device comprising

(i) an electrophoretic fluid which fluid comprises a first type ofparticles, a second type of particles and a third type of particles, allof which are dispersed in a solvent or solvent mixture, wherein thefirst type of particles carry a charge polarity while the second andthird types of particles carry opposite charge polarity, and

(ii) a plurality of pixels wherein each pixel is sandwiched between acommon electrode and a pixel electrode, which method comprises

a) applying no voltage to the pixel electrodes and applying a highvoltage to the common electrode wherein the high voltage has a polarityopposite of the charge polarity of the first type of particles, to driveall pixels towards the color state of the first type of particles;

b) applying no voltage to the pixel electrodes and applying a lowvoltage to the common electrode wherein the low voltage has a polarityopposite of the charge polarity of the third type of particles, to driveall pixels towards the color state of the third type of particles; and

c) maintaining the common electrode grounded and applying differentvoltages to the pixel electrodes to drive pixels towards their desiredcolor states.

In one embodiment, in step (c), no voltage is applied to the pixelelectrodes to maintain the pixels in the color state of the third typeof particles.

In one embodiment, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the secondtype of particles to drive the pixels towards the color state of thesecond type of particles.

In one embodiment, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the firsttype of particles to drive the pixels towards the color state of thefirst type of particles.

In one embodiment, the method further comprises a shaking waveform priorto step (a).

In one embodiment, the first type of particles is negatively charged andthe second and third types of particles are positively charged.

In one embodiment, the first type of particles is white particles, thesecond type of particles is black particles and the third type ofparticles is non-white and non-black particles.

A second aspect of the invention is directed to a driving method for adisplay device comprising

(i) an electrophoretic fluid which fluid comprises a first type ofparticles, a second type of particles, a third type of particles and afourth type of particles, all of which are dispersed in a solvent orsolvent mixture, wherein the first and second types of particles areoppositely charged and the third and fourth types of particles areoppositely charged, and

(ii) a plurality of pixels wherein each pixel is sandwiched between acommon electrode and a pixel electrode, which method comprises

a) applying no voltage to the pixel electrodes and applying a highvoltage to the common electrode wherein the high voltage has a polarityopposite of the charge polarity of the second type of particles, todrive all pixels towards the color state of the second type ofparticles;

b) applying no voltage to the pixel electrodes and applying a lowvoltage to the common electrode wherein the low voltage has a polarityopposite of the charge polarity of the third type of particles, to driveall pixels towards the color state of the third type of particles; and

c) maintaining the common electrode grounded and applying differentvoltages to the pixel electrodes to drive pixels towards their desiredcolor states.

In one embodiment, in step (c), no voltage is applied to the pixelelectrodes to maintain the pixels in the color state of the third typeof particles.

In one embodiment, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the firsttype of particles to drive the pixels towards the color state of thefirst type of particles.

In one embodiment, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the secondtype of particles to drive the pixels towards the color state of thesecond type of particles.

In one embodiment, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the firsttype of particles, followed by applying a low voltage to the pixelelectrodes wherein the low voltage has the same polarity as the fourthtype of particles to drive the pixels towards the color state of thefourth type of particles.

In one embodiment, the method further comprises a shaking waveform priorto step (a).

In one embodiment, the first and third types of particles are positivelycharged and the second and fourth types of particles are negativelycharged.

In one embodiment, the first type of particles is black particles, thesecond type of particles is yellow particles, the third type ofparticles is red particles and the fourth type of particles is whiteparticles.

In one embodiment, the first type of particles is high positiveparticles, the second type of particles is high negative particles, thethird type of particles is low positive particles and the fourth type ofparticles is low negative particles.

A third aspect of the invention is directed to a driving method for acolor display device comprising a plurality of pixels, wherein each ofthe pixels is sandwiched between a common electrode and a pixelelectrode, the method comprises:

a) driving all pixels towards a color state by modulating only thecommon electrode; and

b) driving all pixels towards their desired color states by maintainingthe common electrode grounded and applying different voltages to thepixel electrodes.

In one embodiment, the method further comprises a shaking waveform.

A fourth aspect of the invention is directed to a backplane system fordriving a display device comprising an electrophoretic fluid wherein thefluid comprises a first type of particles, a second type of particlesand a third type of particles, all of which are dispersed in a solventor solvent mixture, wherein the first type of particles carry a chargepolarity while the second and third types of particles carry oppositecharge polarity, which backplane system has only three levels ofvoltage, 0V, a high positive voltage and a high negative voltage.

A fifth aspect of the invention is directed to a backplane system fordriving a display device comprising an electrophoretic fluid wherein thefluid comprises a first type of particles, a second type of particles, athird type of particles and a fourth type of particles, all of which aredispersed in a solvent or solvent mixture, wherein the first and secondtypes of particles are oppositely charged and the third and fourth typesof particles are oppositely charged, which backplane system has onlyfour levels of voltage, 0V, a high positive voltage, a high negativevoltage and a low positive voltage or a low negative voltage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts a display layer of the present invention.

FIG. 2 depicts an electrophoretic fluid comprising three types ofparticles.

FIGS. 3A-3B illustrate the driving sequence of the three particle fluidsystem.

FIGS. 4 a, 4 b and 5 illustrate a driving method of the presentinvention for the three particle fluid system.

FIG. 6 depicts an electrophoretic fluid comprising four types ofparticles.

FIGS. 7A-7C illustrate the driving sequence of the four particle fluidsystem.

FIGS. 8 a, 8 b and 9 illustrate a driving method of the presentinvention for the four particle fluid system.

FIGS. 10 a, 11 a and 12 a are diagrams for implementation of the presentdriving methods.

FIGS. 10 b, 11 b and 12 b are diagrams for the prior art drivingmethods.

DETAILED DESCRIPTION OF THE INVENTION General:

A display fluid of the present invention may comprise three or fourtypes of particles. The multiple types of particles may be of any colorsas long as the colors are visually distinguishable. In the fluid, theparticles are dispersed in a solvent or solvent mixture.

For white particles, they may be formed from an inorganic pigment, suchas TiO₂, ZrO₂, ZnO, Al₂O₃, Sb₂O₃, BaSO₄, PbSO₄ or the like.

For black particles, they may be formed from CI pigment black 26 or 28or the like (e.g., manganese ferrite black spinel or copper chromiteblack spinel) or carbon black.

The colored particles (non-white and non-black) may be of a color suchas red, green, blue, magenta, cyan or yellow. The pigments for this typeof particles may include, but are not limited to, CI pigment PR 254,PR122, PR149, PG36, PG58, PG7, PB28, PB15:3, PY138, PY150, PY155 andPY20. These are commonly used organic pigments described in color indexhandbooks, “New Pigment Application Technology” (CMC Publishing Co, Ltd,1986) and “Printing Ink Technology” (CMC Publishing Co, Ltd, 1984).Specific examples include Clariant Hostaperm Red D3G 70-EDS, HostapermPink E-EDS, PV fast red D3G, Hostaperm red D3G 70, Hostaperm BlueB2G-EDS, Hostaperm Yellow H4G-EDS, Hostaperm Green GNX, BASF Irgazinered L 3630, Cinquasia Red L 4100 HD, and Irgazin Red L 3660 HD; SunChemical phthalocyanine blue, phthalocyanine green, diarylide yellow ordiarylide AAOT yellow.

In addition to the colors, the multiple types of particles may haveother distinct optical characteristics, such as optical transmission,reflectance, luminescence or, in the case of displays intended formachine reading, pseudo-color in the sense of a change in reflectance ofelectromagnetic wavelengths outside the visible range.

A display layer utilizing a display fluid of the present invention, asshown in FIG. 1, has two surfaces, a first surface (13) on the viewingside and a second surface (14) on the opposite side of the first surface(13). The display fluid is sandwiched between the two surfaces. On theside of the first surface (13), there is a common electrode (11) whichis a transparent electrode layer (e.g., ITO), spreading over the entiretop of the display layer. On the side of the second surface (14), thereis an electrode layer (12) which comprises a plurality of pixelelectrodes (12 a).

The pixel electrodes are described in U.S. Pat. No. 7,046,228, thecontent of which is incorporated herein by reference in its entirety. Itis noted that while active matrix driving with a thin film transistor(TFT) backplane is mentioned for the layer of pixel electrodes, thescope of the present invention encompasses other types of electrodeaddressing as long as the electrodes serve the desired functions.

Each space between two dotted vertical lines in FIG. 1 denotes a pixel.As shown, each pixel has a corresponding pixel electrode. An electricfield is created for a pixel by the potential difference between avoltage applied to the common electrode and a voltage applied to thecorresponding pixel electrode.

The multiple types of particles may have different charge levels. In oneembodiment, the weaker charged particles have charge intensity beingless than about 50%, or about 5% to about 30%, the charge intensity ofthe stronger charged particles. In another embodiment, the weakercharged particles have charge intensity being less than about 75%, orabout 15% to about 55%, the charge intensity of the stronger chargedparticles. In a further embodiment, the comparison of the charge levelsas indicated applies to two types of particles having the same chargepolarity.

The charge intensity may be measured in terms of zeta potential. In oneembodiment, the zeta potential is determined by Colloidal DynamicsAcoustoSizer IIM with a CSPU-100 signal processing unit, ESA EN# Attnflow through cell (K:127). The instrument constants, such as density ofthe solvent used in the sample, dielectric constant of the solvent,speed of sound in the solvent, viscosity of the solvent, all of which atthe testing temperature (25° C.) are entered before testing. Pigmentsamples are dispersed in the solvent (which is usually a hydrocarbonfluid having less than 12 carbon atoms), and diluted to between 5-10% byweight. The sample also contains a charge control agent (Solsperse®17000, available from Lubrizol Corporation, a Berkshire Hathawaycompany), with a weight ratio of 1:10 of the charge control agent to theparticles. The mass of the diluted sample is determined and the sampleis then loaded into the flow through cell for determination of the zetapotential.

If there are two pairs of high-low charge particles in the same fluid,the two pairs may have different levels of charge differentials. Forexample, in one pair, the low positively charged particles may have acharge intensity which is 30% of the charge intensity of the highpositively charged particles. In another pair, the low negativelycharged particles may have a charge intensity which is 50% of the chargeintensity of the high negatively charged particles.

The solvent in which the multiple types of particles are dispersed isclear and colorless. It preferably has a low viscosity and a dielectricconstant in the range of about 2 to about 30, preferably about 2 toabout 15 for high particle mobility. Examples of suitable dielectricsolvent include hydrocarbons such as isopar, decahydronaphthalene(DECALIN), 5-ethylidene-2-norbornene, fatty oils, paraffin oil, siliconfluids, aromatic hydrocarbons such as toluene, xylene,phenylxylylethane, dodecylbenzene or alkylnaphthalene, halogenatedsolvents such as perfluorodecalin, perfluorotoluene, perfluoroxylene,dichlorobenzotrifluoride, 3,4,5-trichlorobenzotri fluoride,chloropentafluoro-benzene, dichlorononane or pentachlorobenzene, andperfluorinated solvents such as FC-43, FC-70 or FC-5060 from 3M Company,St. Paul Minn., low molecular weight halogen containing polymers such aspoly(perfluoropropylene oxide) from TCI America, Portland, Oreg.,poly(chlorotrifluoro-ethylene) such as Halocarbon Oils from HalocarbonProduct Corp., River Edge, N.J., perfluoropolyalkylether such as Galdenfrom Ausimont or Krytox Oils and Greases K-Fluid Series from DuPont,Del., polydimethylsiloxane based silicone oil from Dow-corning (DC-200).

In the present invention, at least one type of particles may demonstratean electric field threshold. In one embodiment, one type of the highercharged particles has an electric field threshold.

The term “electric field threshold”, in the context of the presentinvention, is defined as the maximum electric field that may be appliedfor a period of time (typically not longer than 30 seconds, preferablynot longer than 15 seconds), to a group of particles, without causingthe particles to appear at the viewing side of a pixel, when the pixelis driven from a color state different from the color state of the groupof particles. The term “viewing side”, in the present application,refers to the first surface in a display layer where images are seen bythe viewers.

The electric field threshold is either an inherent characteristic of thecharged particles or an additive-induced property.

In the former case, the electric field threshold is generated, relyingon certain attraction force between oppositely charged particles orbetween particles and certain substrate surfaces.

In the case of additive-induced electric field threshold, a thresholdagent which induces or enhances the threshold characteristics of anelectrophoretic fluid may be added. The threshold agent may be anymaterial which is soluble or dispersible in the solvent or solventmixture of the electrophoretic fluid and carries or induces a chargeopposite to that of the charged particles. The threshold agent may besensitive or insensitive to the change of applied voltage. The term“threshold agent” may broadly include dyes or pigments, electrolytes orpolyelectrolytes, polymers, oligomers, surfactants, charge controllingagents and the like.

Three Particle System:

FIG. 2 depicts a three particle fluid system as described in US2014-0092466; the content of which is incorporated herein by referencein its entirety.

The electrophoretic fluid comprises three types of particles dispersedin a dielectric solvent or solvent mixture. For ease of illustration,the three types of particles may be referred to as a first type ofparticles, a second type of particles and a third type of particles. Asan example shown in FIG. 2, the first type of particles is whiteparticles (W); the second type of particles is black particles (K); andthe third type of particles is red particles (R). The third type ofparticles can be any colors of non-white and non-black.

Two of the three types of particles (i.e., the first and second types ofparticles) have opposite charge polarities and the third type ofparticles carries the same charge polarity as one of the other two typesof particles. For example, if the black particles are positively chargedand the white particles are negatively charged, and then the redparticles are either positively charged or negatively charged.

FIG. 3 demonstrates the driving sequence of this type of color displaydevice. For illustration purpose, the white particles (W) are negativelycharged while the black particles (K) are positively charged. The redparticles (R) carry the same charge polarity as the black particles (K).

Because of the attraction force between the black and white particles,the black particles (K) are assumed to have an electric field thresholdof lV. Therefore, the black particles would not move to the viewing sideif an applied voltage potential difference is lV or lower.

The red particles carry a charge weaker than that of the black and whiteparticles. As a result, the black particles move faster than the redparticles (R), when an applied voltage potential is higher than lVbecause of the stronger charge carried by the black particles.

In FIG. 3 a, a high positive voltage potential difference, +hV, isapplied. In this case, the white particles (W) move to be near or at thepixel electrode (32 a) and the black particles (K) and the red particles(R) move to be near or at the common electrode (31). As a result, ablack color is seen at the viewing side. The red particles (R) movetowards the common electrode (31); however because they carry lowercharge, they move slower than the black particles (K).

In FIG. 3 b, when a high negative potential difference, −hV, is applied,the white particles (W) move to be near or at the common electrode (31)and the black particles (K) and the red particles (R) move to be near orat the pixel electrode (32 a). As a result, a white color is seen at theviewing side. The red particles (R) move towards the pixel electrodebecause they are also positively charged. However, because of theirlower charge intensity, they move slower than the black particles.

In FIG. 3 c, a low positive voltage potential difference, +lV, isapplied to the pixel of FIG. 3 a (i.e., driving from the white colorstate). In this case, the negatively charged white particles (W) in FIG.3 a move towards the pixel electrode (32 a). The black particles (K)move little because of their electric field threshold being lV. Due tothe fact that the red particles (R) do not have a significant electricfield threshold, they move to be near or at the common electrode (31)and as a result, a red color is seen at the viewing side.

It is noted that the lower voltage (+lV or −lV) applied usually has amagnitude of about 5% to about 50% of the magnitude of the full drivingvoltage required to drive the pixel from the black state to the whitestate (−hV) or from the white state to the black state (+hV). In oneembodiment, +hV and −hV may be +15V and −15V, respectively and +lV and−lV may be +3V and −3V, respectively. In addition, it is noted that themagnitudes of +hV and −hV may be the same or different. Likewise, themagnitude of +lV and −lV may be the same or different.

The term “driving voltage potential difference” refers to the voltagedifference between the common electrode and a pixel electrode. In theprevious driving method, the common electrode shared by all pixelsremains grounded and each pixel is driven by the voltage applied to thecorresponding pixel electrode. If such an approach is used to drive thefluid system as described in FIGS. 2 and 3, the backplane system wouldneed to have each pixel electrode at at least four different levels ofvoltages, 0V, +hV, −hV and +lV. Such a backplane system is costly toimplement, which is explained in a section below.

The present inventors now propose a new driving method where thebackplane system is simplified while color states of high quality canstill be displayed.

FIGS. 4 a and 4 b illustrate the initial step of the present drivingmethod and this step is applied to all pixels. A shaking waveform isfirst applied, after which in phase I, the common electrode shared byall pixels is applied a +hV while all pixel electrodes are at 0V,resulting in a driving voltage potential difference of −hV for allpixels, which drive all of them towards the white state (see FIG. 3 a).In phase II, −lV is applied to the common electrode while all pixelelectrodes still remain at 0V, resulting in a driving voltage potentialdifference of +lV, which drives all pixels towards the red state (seeFIG. 3 c). In this initial step, all pixel electrodes remain at 0V whilethe common electrode is modulated, switching from +hV to −lV.

The shaking waveform applied before phase I consists of a pair ofopposite driving pulses for many cycles. For example, the shakingwaveform may consist of a +15V pulse for 20 msec and a −15V pulse for 20msec and such a pair of pulses is repeated for 50 times. The total timeof such a shaking waveform would be 2000 msec.

With this added shaking waveform, the color state (i.e., red) can besignificantly better than that without the shaking waveform, on bothcolor brightness and color purity. This is an indication of betterseparation of the white particles from the red particles as well as theblack particles from the red particles.

Each of the driving pulses in the shaking waveform is applied for notexceeding half of the driving time from the full black state to the fullwhite state or vice versa. For example, if it takes 300 msec to drive adisplay device from a full black state to a full white state or viceversa, the shaking waveform may consist of positive and negative pulses,each applied for not more than 150 msec. In practice, it is preferredthat the pulses are shorter.

FIG. 5 illustrates the next step of the driving method. In this step,all pixels are driven simultaneously to their desired color states. Inthis step, the common electrode is grounded at 0V while differentvoltages are applied to the pixel electrodes. For pixels that remain inthe red state, no voltage is applied to the corresponding pixelelectrodes, resulting in no driving voltage potential difference. Forpixels to be in the black state, a +hV is applied to the correspondingpixel electrodes. For pixels to be in the white state, a −hV is appliedto the corresponding pixel electrodes.

With this driving method in which the common electrode is modulated inthe initial step, the backplane system would only need to have eachpixel electrode at three different levels of voltage, 0V, +hV and −hV,which is much simplified than the backplane system used in the previousmethod.

FIG. 10 a is a simplified diagram illustrating the implementation of thepresent driving method. As shown, there are three different levels ofvoltage, 0V, +hV and −lV, which may be applied to the common electrode(Vcom) and there are three different levels of voltage, 0V, +hV and −hV,which may be applied to a pixel electrode.

FIG. 10 b is a diagram illustrating the corresponding prior art method.In this diagram, there are three levels of voltage, +hV, −hV and +lV,which may be applied to a pixel electrode. Commercially available TFTbackplane usually only has source IC which supports 0V, +hV and −hV.Therefore if the prior art method is utilized, there would be the needto modify the source IC to support an additional voltage option of +lVapplied to the pixel electrode.

Four Types of Particles:

FIG. 6 depicts an alternative display device in which theelectrophoretic fluid comprises four types of particles dispersed in adielectric solvent or solvent mixture, as described in U.S. ProvisionalApplication No. 61/824,887, which is incorporated herein by reference inits entirety. For ease of illustration, the four types of particles maybe referred to as a first type of particles, a second type of particles,a third type of particles and a fourth type of particles. As an exampleshown in FIG. 6, the first type of particles is black particles (K); thesecond type of particles is yellow particles (Y); the third type ofparticles is red particles (R); and the fourth type of particles iswhite particles (W).

In this example, the black and yellow particles carry opposite chargepolarities. For example, if the black particles are positively charged,the yellow particles are negatively charged. The red and white particlesare also oppositely charged. However the charges carried by the blackand yellow particles are stronger than the charges carried by the redand white particles.

For example, the black particles (K) carry a high positive charge; theyellow particles (Y) carry a high negative charge; the red (R) particlescarry a low positive charge; and the white particles (W) carry a lownegative charge. The driving sequence of this type of color displaydevice is shown in FIG. 7.

In FIG. 7 a, when a high negative voltage potential difference (e.g.,−hV) is applied to a pixel, the yellow particles (Y) are pushed to thecommon electrode (71) side and the black particles (K) are pulled to thepixel electrode (72 a) side. The red (R) and white (W) particles, due totheir lower charge levels, move slower than the higher charged black andyellow particles and therefore they stay between the common electrodeand the pixel electrode, with white particles above the red particles.As a result, a yellow color is seen at the viewing side.

In FIG. 7 b, when a high positive voltage potential difference (e.g.,+hV) is applied to the pixel, the particle distribution would beopposite of that shown in FIG. 7 a and as a result, a black color isseen at the viewing side.

In FIG. 7 c, when a lower positive voltage potential difference (e.g.,+lV) is applied to the pixel of FIG. 7 a (that is, driven from theyellow state), the yellow particles (Y) move towards the pixel electrode(72 a) while the black particles (K) move towards the common electrode(71). However, when they meet while moving, because of their strongattraction to each other, they stop moving and remain between the commonelectrode and the pixel electrode. The lower charged (positive) redparticles (R) move all the way towards the common electrode (71) side(i.e., the viewing side) and the lower charged (negative) whiteparticles (W) move towards the pixel electrode (72 a) side. As a result,a red color is seen.

In FIG. 7 d, when a lower negative voltage potential difference (e.g.,−lV) is applied to the pixel of FIG. 7 b (that is, driven from the blackstate), the black particles (K) move towards the pixel electrode (72 a)while the yellow particles (Y) move towards the common electrode (71).When the black and yellow particles meet, because of their strongattraction to each other, they stop moving and remain between the commonelectrode and the pixel electrode. The lower charged (negative) whiteparticles (W) move all the way towards the common electrode side (i.e.,the viewing side) and the lower charged (positive) red particles (R)move towards the pixel electrode side. As a result, a white color isseen.

It is also noted that in FIGS. 7 c and 7 d, while the low drivingvoltages applied (+lV or −lV) are not sufficient to separate thestronger charged black and yellow particles, they, however, aresufficient to separate, not only the two types of oppositely chargedparticles of lower charge intensity, but also the lower chargedparticles from the stronger charged particles of opposite chargepolarity.

It is noted that the lower voltage (+lV or −lV) applied usually has amagnitude of about 5% to about 50% of the magnitude of the full drivingvoltage required to drive the pixel from the black state to the yellowstate (−hV) or from the yellow state to the black state (+hV). In oneembodiment, +hV and −hV may be +15V and −15V, respectively and +lV and−lV may be +3V and −3V, respectively. In addition, it is noted that themagnitudes of +hV and −hV may be the same or different. Likewise, themagnitude of +lV and −lV may be the same or different.

FIGS. 8 a and 8 b illustrate the initial step of the present drivingmethod for the four particle system and this step is applied to allpixels. In phase I, the common electrode shared by all pixels is applieda +hV while all pixel electrodes are at 0V, resulting in a drivingvoltage potential difference of −hV for all pixels which drive all ofthem to the yellow state. In phase II, −lV is applied to the commonelectrode while all pixel electrodes still remain at 0V, resulting in adriving voltage potential difference of +lV, which drives all pixels tothe red state. In this initial step, all pixel electrodes remain at 0Vwhile the common electrode is modulated, switching from +hV to −lV.

The shaking waveforms as described for FIG. 4 may also be applied inthis case.

FIG. 9 illustrates the next step of the driving method. In this step,the common electrode is grounded at 0V while different voltages areapplied to the pixel electrodes. For pixels to remain in the red state,no voltage is applied to the corresponding pixel electrodes, resultingin no driving voltage potential difference. For pixels to be in theblack state, a +hV is applied to the corresponding pixel electrodes. Forpixels to be in the yellow state, a −hV is applied to the correspondingpixel electrodes. For pixels to be in the white state, a +hV, followedby a −lV is applied to the corresponding pixels.

With this driving method in which the common electrode is modulated inthe initial step, the backplane system would only need to have eachpixel electrode at four different levels of voltage, 0V, +hV, −hV and−lV which is much simplified than the backplane system used in theprevious method in which the system would be required to have each pixelat five different levels of voltage, 0V, +hV, −hV, +lV and −lV.

FIG. 11 a is a simplified diagram illustrating the implementation of thepresent driving method. As shown, there are three different levels ofvoltage, 0V, +hV and −lV, which may be applied to the common electrode(Vcom) and there are four different levels of voltage, 0V, +hV, −hV and−lV, which may be applied to the pixel electrode.

FIG. 11 b is a diagram illustrating the corresponding prior art method.In this diagram, there are four levels of voltage, +hV, −hV, +lV and−lV, which may be applied to a pixel electrode. Commercially availableTFT backplane usually only has source IC which supports 0V, +hV and −hV.Therefore if the prior art method is utilized, there would be the needto modify the source IC to support one additional voltage option of +lVapplied to the pixel electrode, compared to the present driving method.

In the illustration above, in the initial step, all pixels are driven tothe red state. However it is also possible to drive all pixels to thewhite state in the initial step (by keeping the pixel electrodes groundsand applying a −hV followed by +lV to the common electrode), followed bydriving pixels to be black from white to black (+hV), driving pixels tobe yellow from white to yellow (−hV), and applying no driving voltagepotential difference to white pixels to remain white. The pixels to bered are driven from white to yellow (−hV) and then from yellow to red(+lV). In this scenario, the backplane system would only need to haveeach pixel electrode at four different levels of voltage, 0V, +hV, −hVand +lV.

FIG. 12 a is a simplified diagram illustrating the implementation of thepresent driving method. As shown, there are three different levels ofvoltage, 0V, −hV and +lV, which may be applied to the common electrode(Vcom) and there are four different levels of voltage, 0V, +hV, −hV and+lV, which may be applied to the pixel electrode.

FIG. 12 b is a diagram illustrating the corresponding prior art method.In this diagram, there are four levels of voltage, +hV, −hV, +lV and−lV, which may be applied to a pixel electrode. Commercially availableTFT backplane usually only has source IC which supports 0V, +hV and −hV.Therefore if the prior art method is utilized, there would be the needto modify the source IC to support one additional voltage option of −lVapplied to the pixel electrode, compared to the present driving method.

While the present invention has been described with reference to thespecific embodiments thereof, it should be understood by those skilledin the art that various changes may be made and equivalents may besubstituted without departing from the true spirit and scope of theinvention. In addition, many modifications may be made to adapt aparticular situation, materials, compositions, processes, process stepor steps, to the objective and scope of the present invention. All suchmodifications are intended to be within the scope of the claims appendedhereto.

What is claimed is:
 1. A driving method for a display device, whereinthe display device comprises: (i) an electrophoretic fluid comprising afirst type of particles, a second type of particles, and a third type ofparticles, all of which are dispersed in a solvent or solvent mixture,wherein the first type of particles carry a charge polarity while thesecond and third types of particles carry an opposite charge polarity,and (ii) a plurality of pixels wherein each pixel is sandwiched betweena common electrode and a pixel electrode; the method comprises the stepsof: a) applying no voltage to the pixel electrodes and applying a highvoltage to the common electrode, wherein the high voltage has a polarityopposite to the charge polarity of the first type of particles, to driveall pixels towards the color state of the first type of particles; b)applying no voltage to the pixel electrodes and applying a low voltageto the common electrode, wherein the low voltage has a polarity oppositeto the charge polarity of the third type of particles, to drive allpixels towards the color state of the third type of particles; and c)maintaining the common electrode grounded and applying differentvoltages to the pixel electrodes to drive pixels towards their desiredcolor states.
 2. The driving method of claim 1, in step (c), no voltageis applied to the pixel electrodes to maintain the pixels in the colorstate of the third type of particles.
 3. The driving method of claim 1,in step (c), a high voltage is applied to the pixel electrodes whereinthe high voltage has the same polarity as the second type of particlesto drive the pixels towards the color state of the second type ofparticles.
 4. The driving method of claim 1, in step (c), a high voltageis applied to the pixel electrodes wherein the high voltage has the samepolarity as the first type of particles to drive the pixels towards thecolor state of the first type of particles.
 5. The driving method ofclaim 1, further comprising a shaking waveform prior to step (a).
 6. Thedriving method of claim 1, wherein the first type of particles isnegatively charged and the second and third types of particles arepositively charged.
 7. The driving method of claim 1, wherein the firsttype of particles is white particles, the second type of particles isblack particles and the third type of particles is non-white andnon-black particles.
 8. A driving method for a display device, whereinthe display device comprises: (i) an electrophoretic fluid comprising afirst type of particles, a second type of particles, a third type ofparticles and a fourth type of particles, all of which are dispersed ina solvent or solvent mixture, wherein the first and second types ofparticles are oppositely charged and the third and fourth types ofparticles are oppositely charged, and (ii) a plurality of pixels whereineach pixel is sandwiched between a common electrode and a pixelelectrode; the method comprises the steps of: a) applying no voltage tothe pixel electrodes and applying a high voltage to the common electrodewherein the high voltage has a polarity opposite of the charge polarityof the second type of particles, to drive all pixels towards the colorstate of the second type of particles, b) applying no voltage to thepixel electrodes and applying a low voltage to the common electrodewherein the low voltage has a polarity opposite of the charge polarityof the third type of particles, to drive all pixels towards the colorstate of the third type of particles, and c) maintaining the commonelectrode grounded and applying different voltages to the pixelelectrodes to drive pixels towards their desired color states.
 9. Thedriving method of claim 8, in step (c), no voltage is applied to thepixel electrodes to maintain the pixels in the color state of the thirdtype of particles.
 10. The driving method of claim 8, in step (c), ahigh voltage is applied to the pixel electrodes wherein the high voltagehas the same polarity as the first type of particles to drive the pixelstowards the color state of the first type of particles.
 11. The drivingmethod of claim 8, in step (c), a high voltage is applied to the pixelelectrodes wherein the high voltage has the same polarity as the secondtype of particles to drive the pixels towards the color state of thesecond type of particles.
 12. The driving method of claim 8, in step(c), a high voltage is applied to the pixel electrodes wherein the highvoltage has the same polarity as the first type of particles, followedby applying a low voltage to the pixel electrodes wherein the lowvoltage has the same polarity as the fourth type of particles to drivethe pixels towards the color state of the fourth type of particles. 13.The driving method of claim 8, further comprising a shaking waveformprior to step (a).
 14. The driving method of claim 8, wherein the firstand third types of particles are positively charged and the second andfourth types of particles are negatively charged.
 15. The driving methodof claim 8, wherein the first type of particles is black particles, thesecond type of particles is yellow particles, the third type ofparticles is red particles and the fourth type of particles is whiteparticles.
 16. The driving method of claim 8, wherein the first type ofparticles is high positive particles, the second type of particles ishigh negative particles, the third type of particles is low positiveparticles and the fourth type of particles is low negative particles.17. A driving method for a color display device comprising a pluralityof pixels, wherein each of the pixels is sandwiched between a commonelectrode and a pixel electrode; the method comprises: a) driving allpixels towards a color state by modulating only the common electrode,and b) driving all pixels towards their desired color states bymaintaining the common electrode grounded and applying differentvoltages to the pixel electrodes.
 18. The method of claim 17, furthercomprising a shaking waveform.
 19. A backplane system for driving adisplay device comprising an electrophoretic fluid comprising a firsttype of particles, a second type of particles and a third type ofparticles, all of which are dispersed in a solvent or solvent mixture,wherein the first type of particles carry a charge polarity while thesecond and third types of particles carry an opposite charge polarity;the backplane system has only three levels of voltage, 0V, a highpositive voltage and a high negative voltage.